Mr Morgan claimed his actions had been a ‘subconscious last-ditch attempt’ to protect the school from an imminent Ofsted inspection.

“I was horrified when I looked at what I had done but then I could not go back,” he said in a statement.

Mr Morgan, who had been a teacher since 1974, then claimed to have a ‘limited’ recollection of amending some scripts, having been under ‘immense stress’ at the time.

Yet a National College of Teaching and Leadership (NCTL) panel said Mr Morgan’s explanation was not credible.

A report of the hearing said: “In the panel’s view, it would have taken some time for Mr Morgan to go through the papers, check children’s answers and make the significant number of amendments that he did.

"His actions were not committed in a moment of 'sheer madness', but would have taken some time, and occurred over several days during that week of 12 to 15 May 2014.”

Mr Morgan was found guilty of unacceptable professional conduct and struck off indefinitely.

However, the panel said Mr Morgan could seek to have it lifted after five years.

“Mr Morgan has shown regret and remorse for the impact of his actions,” the findings said.

“Mr Morgan accepted responsibility for the annulment of the results early on, and has begun the process of self-reflection and understanding his actions.”

Mr Morgan, who had been a head at St John’s since 2001, retired from the school in 2014.